Several known systems use force transducers of different types to monitor force applied manually to a limb. In most cases, force is measured uni-directionally i.e. the push-force or the pull-force is measured, but not both, through a pad or plate applied to a limb. This type of clinical device does not allow the force to be measured during both the push and pull phases of testing cycles characteristic of a clinical evaluation. Some myometers allow for push or pull measurement but this requires the use of either a pad for push or a hook for pull. Numerous laboratory-based systems have been described in which limbs are held in a cast or cradle, and a force transducer measures push-pull forces applied to the cast. Methods of measuring the dynamic characteristics of muscle rigidity, strength and tremor in the upper extremity are described by J. Ghika et al in IEEE Trans. Biomed. Eng. 40, pages 276-283 (1993) and by M. P. Caligiuri in Movement Disorder, Vol. 9, pages 57-63 (1994). Several myometers incorporate bulbs or pads inflated with air or fluid. Force applied to the bulb or pad is measured indirectly by a pressure transducer sensing pressure in a port or tube leading from the bulb.
U.S. Pat. No. 4,337,780 discloses an evaluator's glove having pads attached to the fingertip and palm areas. The evaluator operates a valve to selectively connect one or the other of the pads to a pressure transducer. The force applied to the selected pad is evaluated. IEEE Transactions on Biomedical Engineering 35 (1988) December p. 1091-1093, discloses a plurality of force-sensing elements attached to the fingertips of a clinician performing vaginal delivery of babies. The contribution of the individual fingers to the total grasping force is monitored.
None of these devices allow a clinician to grasp the limb between thumb and fingers and apply cyclical push and pull forces. This is a crucial difference, because in order to evaluate limb stiffness, it is important for the evaluator to cycle the limb back and forth through the full range of motion, while supporting it in a manual grasp. To our knowledge, no myometer exists which ignores the internal force of the grasp while registering the resultant force exerted on the limb.